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These rambling words are Work-In-Progress.

Questions to ask when defining a self-sizing view or cell

  1. Is it a self-satisfied view? That is, do its internal constraints suffice to define what size it would want to be if external constraints only positioned it on screen?

    This question may be equivalent to the following questions:

    • If external constraints only set its center, then would it return a valid value to the call systemLayoutSizeFittingSize(UILayoutFittingCompressedSize)?

    • If external constraints only set its center, then would it return a valid value to the call sizeThatFits?

    • Does it return a valid value to intrinsicContentSize? Or is this method only supposed to be defined for leaf views? Does it by default return a sensible value for composite views? (Maybe: implementing intrinsicContentSize is how to make a leaf view self-satisifed, and implementing an axial chain of constraints is what suffices to make a composite view self-satisfied.)

    • For both the vertical and horizontal axis, does the view have a chain of constraints that bind one edge to its opposite edge?

  2. If external constraints squeezed the view to be smaller than its preferred size, or stretched it to be bigger than its preferred size, then something in the view has got to give. That is, some constraint has got to give. Do the priorities of the view's internal constraints clearly defines which ones take precedence in these situations? If not, then the view's constraints are ambiguous in combination with certain external constraints.

preferred content size, self-satisfied views, and priorities

Let us try to define some terms unambiguously.

A view's preferred content size is the size it would take if you set only its position, and allowed AL to size it further.

The key question for self-sizing cells, or for views in general, is is the preferred content size well-defined?

How do we define it? A leaf view defines its preferred size by implementing intrinsicContentSize, which computes a size based on the view's content. Here "content" does not mean subviews, but some kind of raw material that is not managed by AL, like an image or a string. A non-leaf view has a preferred content size if it is self-satified, that is, if it implements a chain of constraints for both the horizontal and the vertical axis.

A view is self-satisfied if it establishes a preferred size in the absence of external constraints. This is binary: a view either is or is not self-satisfied.

However, it is also important for a view to specify it's preferred size and layout in the presence of external constraints on its size. But this is not a binary question. Rather, the question is if the view defines a preferred size for a given set of external constraints on its size. So a view may establish a preferred layout given external constraints confining the view within a certain range of possible fitting sizes, but fail to define a preferred size and internal layout if external constraints squeeze it or stretch it beyond a certain degree.